[en] Epitaxial ultrathin films of the metallic perovskite LaNiO₃ were grown on (001) SrTiO₃ substrates using off-axis rf magnetron sputtering. The film structure was characterized and their electrical properties investigated. Films thinner than 8 unit cells display a metal-insulator transition at a thickness dependent characteristic temperature. Hall measurements revealed p-type conduction, which was confirmed by electric field-effect experiments. Large changes in the transport properties and the metal-insulator transition temperature were observed for the thinnest LaNiO₃ films as the carrier density was electrostatically tuned.

[en] We present a brief review of the role of interfacial physics in ferroelectric oxides, with an emphasis on the importance of boundary conditions that determine the properties of very thin ferroelectric films and superlattices. As well as discussing the screening problem, and the role of strain and electrostatics in ferroelectrics, we highlight some of the possibilities in fine period superlattices where the high density of interfaces can lead to new and potentially useful phenomena

[en] Physical and structural phenomena originating from polar discontinuities have generated enormous activity. In the last ten years, the oxide interface between polar $\text{LaAl}{\text{O}}_3$ and non-polar $\text{SrTi}{\text{O}}_3$, both band insulators, has attracted particular interest, as it hosts an electron liquid with remarkable properties: it superconducts, has a sizeable spin–orbit interaction and its properties are tunable by an electric field. The profile of the carrier density at the interface and the exact band structure are properties strongly linked and still objects of debate. Here we review the experimental findings on the origin and the extension of the electron liquid and discuss the theoretical models developed to describe the charge profile and the band structure. We also introduce a model to account for the effect of interface disorder which could modify the charge distribution. (topical review)

[en] Short communication

[en] We report on the structural characterization of LaAlO₃/SrTiO₃ interfaces and on their transport properties. LaAlO₃ films were prepared using pulsed laser deposition onto TiO₂ terminated (001) SrTiO₃ substrates inducing a metallic conduction at the interface. Resistance and Hall effect measurements reveal a sheet carrier density between 0.4 and 1.2 x 10¹⁴ electrons cm^-2 at room temperature and a mobility of ∼300 cm² V^-1 s^-1 at low temperatures. A transition to a superconducting state is observed at a temperature of ∼200 mK. The superconducting characteristics display signatures of 2D superconductivity.

[en] We report a detailed analysis of magneto-transport properties of top- and back-gated LaAlO₃/SrTiO₃ heterostructures. Efficient modulation in magneto-resistance, carrier density, and mobility of the two-dimensional electron liquid present at the interface is achieved by sweeping top and back gate voltages. Analyzing those changes with respect to the carrier density tuning, we observe that the back gate strongly modifies the electron mobility while the top gate mainly varies the carrier density. The evolution of the spin-orbit interaction is also followed as a function of top and back gating

[en] We have studied the electronic properties of the 2D electron liquid present at the LaAlO₃/SrTiO₃ interface in series of samples prepared at different growth temperatures. We observe that interfaces fabricated at 650 °C exhibit the highest low temperature mobility (≈10 000 cm² V⁻¹ s⁻¹) and the lowest sheet carrier density (≈5×10¹² cm⁻²). These samples show metallic behavior and Shubnikov-de Haas oscillations in their magnetoresistance. Samples grown at higher temperatures (800–900 °C) display carrier densities in the range of ≈2−5×10¹³ cm⁻² and mobilities of ≈1000 cm² V⁻¹ s⁻¹ at 4 K. Reducing their carrier density by field effect to 8×10¹² cm⁻² lowers their mobilities to ≈50 cm² V⁻¹ s⁻¹ bringing the conductance to the weak-localization regime

[en] We have performed ferroelectric field effect experiments using an epitaxial heterostructure composed of ferroelectric Pb(Zr_0.2Ti_0.8)O₃ and superconducting Nb-doped SrTiO₃. The films were prepared on (001) SrTiO₃ substrates by off-axis radio-frequency magnetron sputtering and pulsed-laser deposition. By switching the polarization field of the 500-A-thick Pb(Zr_0.2Ti_0.8)O₃ layer, a large change of about 30% in resistivity and a 20% shift of T_c (ΔT_c∼0.05 K) were induced in the 400-A-thick epitaxial Nb-doped SrTiO₃ layer. The relationship between T_c and the electrostatically modulated average carrier concentration can be mapped onto the phase diagram of chemically doped SrTiO₃

[en] This review stands in the larger framework of functional materials by focussing on heterostructures of rare-earth nickelates, described by the chemical formula RNiO₃ where R is a trivalent rare-earth R  =  La, Pr, Nd, Sm, …, Lu. Nickelates are characterized by a rich phase diagram of structural and physical properties and serve as a benchmark for the physics of phase transitions in correlated oxides where electron–lattice coupling plays a key role. Much of the recent interest in nickelates concerns heterostructures, that is single layers of thin film, multilayers or superlattices, with the general objective of modulating their physical properties through strain control, confinement or interface effects. We will discuss the extensive studies on nickelate heterostructures as well as outline different approaches to tuning and controlling their physical properties and, finally, review application concepts for future devices. (review)

[en] Within the last twenty years, the status of the spin–orbit interaction has evolved from that of a simple atomic contribution to a key effect that modifies the electronic band structure of materials. It is regarded as one of the basic ingredients for spintronics, locking together charge and spin degrees of freedom and recently it is instrumental in promoting a new class of compounds, the topological insulators. In this review, we present the current status of the research on the spin–orbit coupling in transition metal oxides, discussing the case of two semiconducting compounds, and , and the properties of surface and interfaces based on these. We conclude with the investigation of topological effects predicted to occur in different complex oxides. (key issues review)